Among prevailing methods of expressing a three-dimensional shape in drawings, there is a method using orthographic views and a method using sectional views. In the method using orthographic views, if local coordinates of a three-dimensional body as an object are determined, orthographic views can be uniquely obtained from those coordinates by projection to the XY-, YZ- and ZX-planes. Therefore, a method of constructing a three-dimensional wireframe structure from the orthographic views is established as an inverse transformation. In this manner, the present inventors have proposed a method of generating a solid model from a three-dimensional wireframe structure using a non-manifold model (Japanese Patent Application No. 4-268650). The present inventors have also proposed a method of constructing a solid model in an interactive manner from incomplete orthographic views (Japanese Patent Application No. 5-184244).
However, in the method using sectional views, due to arbitrariness in taking sectional views, there exists infinite methods of making drawings even if the local coordinates of an object body are determined. Further, since sectional views usually include abbreviated expressions, an original three-dimensional shape cannot be constructed without using the knowledge of such abbreviated expressions in drawings. For the above reasons, it has been conventionally considered very difficult to provide a system of generating a solid model from drawings including an ordinary sectional view.
Published Unexamined Patent Application (PUPA) No. 3-74784 discloses a technique in which sectional views taken by projecting respective parts of a three-dimensional body in the vertical and horizontal directions are input, the respective parts in the input views are divided in accordance with a user's specification, an approximation to a hyper quadratic function is performed on contour data of the divided parts, ratios among values of parameters of respective functions in two input plan views are adjusted for the above-obtained function, and the respective parts are combined in a three-dimensional space based on a positional relationship among the centers of gravity of the respective parts in the two sectional views. However, this technique relates to a means for generating a curved surface from sectional views having hand-written curves, and is not intended to deal with industrial drawings. In this technique, since a solid body approximating the given sectional views is constructed using a hyper quadratic function, the resulting solid body does not necessarily reflect the sectional views in a correct manner. Furthermore, this technique has the disadvantages that it is necessary to divide a single solid body into simpler parts and to input sectional views for each constituent part, and that a part having a hole cannot be expressed due to the nature of hyper quadratic functions.
PUPA No. 4-114282 discloses a technique in which sectional views in configurational feature sections are generated from two-dimensional drawing data, and connection information and features of respective surfaces that constitute a three-dimensional body are extracted from those sectional views. However, this publication is basically directed to conversion from orthographic views to a three-dimensional body, and does not disclose generation of a solid model from sectional views. Although this publication states that sectional views are used, the sectional views merely appear in the process of conversion to a three-dimensional body. Only very simple solid bodies in which basically every surface is parallel with one of the XY-, YZ- and ZX-planes can be processed by this technique. Although this publication states (in the top-right column of page 3) that data of other planes are to be input by the user's instructions, this would require many instructions from a user and is therefore not practical. This statement is associated with the essential difficulties in processing a solid body having a hole or hollow. Although this publication states (in the top-right column of page 3) that the technique is adapted to process a hole in the form of separate processing in accordance with a user's specification, it is more difficult to deal with a hollow. In this technique, an actually existing space is made a logical product of half-spaces in the process of generating a sectional view, but this method is unable to express a hollow.